Numerous methods and systems have been developed for the detection and quantitation of analytes of interest in biochemical and biological substances. Methods and systems which are capable of measuring trace amounts of microorganisms, pharmaceuticals, hormones, viruses, antibodies, nucleic acids and other proteins are of great value to researchers and clinicians.
A very substantial body of art has been developed based upon binding reactions, e.g., antigen-antibody reactions, nucleic acid hybridization techniques, and protein-ligand systems. The high degree of specificity in many biochemical and biological binding systems has led to many assay methods and systems of value in research and diagnostics. Typically, the existence of an analyte of interest is indicated by the presence or absence of an observable “label” attached to one or more of the binding materials.
Electrochemiluminescent (ECL) assays provide a sensitive and precise measurement of the presence and concentration of an analyte of interest. Such techniques use labels or other reactants that can be induced to luminesce when electrochemically oxidized or reduced in an appropriate chemical environment. Such electrochemiluminescence is triggered by a voltage imposed on a working electrode at a particular time and in a particular manner. The light produced by the label is measured and indicates the presence or quantity of the analyte. For a fuller description of such ECL techniques, reference is made to U.S. Pat. Nos. 5,221,605, 5,591,581, 5,597,910, PCT published application WO90/05296, PCT published application WO92/14139, PCT published application WO90/05301; PCT published application WO96/24690, PCT published application U.S.95/03190, PCT application U.S.97/16942, PCT published application U.S.96/06763, PCT published application WO95/08644, PCT published application WO96/06946, PCT published application WO96/33411, PCT published application WO87/06706, PCT published application WO96/39534, PCT published application WO96/41175, PCT published application WO96/40978, PCT/U.S.97/03653 and U.S. patent application Ser. No. 08/437,348 (U.S. Pat. No. 5,679,519). The disclosures of the aforesaid applications are incorporated by reference. Reference is also made to a 1994 review of the analytical applications of ECL by Knight, et al. (Analyst, 1994, 119: 879-890) and the references cited therein. The disclosure of the aforesaid articles are also incorporated by reference.
While electrochemiluminescence assays are significantly improved over chemiluminescence, fluorescence, ELISA and radioisotope-based assays, as well as other assay techniques, there is always a desire to improve assays by increasing the signal or modulation signal obtained from a binding event. By doing so one can improve the ratio of signal to background noise and, therefore, the sensitivity of the assay. Increasing the signal of an ECL assay also has several instrumental advantages including the following: i) less sensitive (and less expensive) light detection systems are required; ii) smaller samples are required; iii) electrodes and instrumentation may be miniaturized so as to allow for instruments that are smaller and/or devices that run many assays concurrently in a small area.